A project is proposed for continuing the development of an ultrasensitive enzyme immunoassay for specific viruses that is expected to be more sensitive than any currently existing technology for that purpose. This proposed assay involves virus-triggered release of microencapsulated enzyme. The assay is noncompetitive, (i.e. it does not involve competition between virus to be detected and labeled viral antigen), involves effective activation of a large number of enzyme molecules for each virus incorporated into the assay system, and is expected to have a very low background. The greatest value of this technology is expected to be for prevention of viral diseases by enabling the user to detect very low levels of pathogenic viruses in, for example, human blood and blood components used for therapeutic applications, and certain foods and water used for human consumption. In the Phase I project, components for this assay system were prepared and preliminary evaluation carried out providing some evidence for its feasibility. The goals of the Phase II project are to develop and optimize this assay system for cytomegalovirus and to determine its sensitivity and other performance characteristics.